Dual clusters of fully connected integrated circuit multiprocessors with shared high-level cache

ABSTRACT

Embodiments of the present invention are directed to managing a shared high-level cache for dual clusters of fully connected integrated circuit multiprocessors. An example of a computer-implemented method includes: providing a drawer comprising a plurality of clusters, each of the plurality of clusters comprising a plurality of processors; providing a shared cache integrated circuit to manage a shared cache memory among the plurality of clusters; receiving, by the shared cache integrated circuit, an operation of one of a plurality of operation types from one of the plurality of processors; and processing, by the shared cache integrated circuit, the operation based at least in part on the operation type of the operation according to a set of rules for processing the operation type.

BACKGROUND

The present invention generally relates to computer system design, andmore specifically, to a managing a shared high-level cache for dualclusters of fully connected integrated circuit multiprocessors.

Symmetric multiprocessing (SMP) systems utilize a multiprocessorhardware and software architecture. Two or more processors are connectedto a single, shared main memory. For example, an SMP system can have acentralized shared memory that operates using a single operating systemwith two or more processors. Each processor can utilize its own cachememory (or simply “cache”) to speed up data access to the shared memoryand to reduce the system bus traffic. Some SMP systems can utilizemultiple cache memories and/or multiple levels of cache memory that maybe shared between and among various processors.

SUMMARY

Embodiments of the present invention are directed to acomputer-implemented method for managing a shared high-level cache fordual clusters of fully connected integrated circuit multiprocessors. Anexample of a computer-implemented method includes: providing a drawercomprising a plurality of clusters, each of the plurality of clusterscomprising a plurality of processors; providing a shared cacheintegrated circuit to manage a shared cache memory among the pluralityof clusters; receiving, by the shared cache integrated circuit, anoperation of one of a plurality of operation types from one of theplurality of processors; and processing, by the shared cache integratedcircuit, the operation based at least in part on the operation type ofthe operation according to a set of rules for processing the operationtype.

Embodiments of the present invention are also directed to a systemcomprising a drawer comprising a plurality of clusters, each of theplurality of clusters comprising a plurality of processors; and a sharedcache integrated circuit to manage a shared cache memory among theplurality of clusters, wherein the shared cache integrated circuit isconfigured to store computer readable instructions and execute thecomputer readable instructions for performing a method, the methodcomprising: receiving, by the shared cache integrated circuit, anoperation of one of a plurality of operation types from one of theplurality of processors, and processing, by the shared cache integratedcircuit, the operation based at least in part on the operation type ofthe operation according to a set of rules for processing the operationtype.

Additional technical features and benefits are realized through thetechniques of the present invention. Embodiments and aspects of theinvention are described in detail herein and are considered a part ofthe claimed subject matter. For a better understanding, refer to thedetailed description and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The specifics of the exclusive rights described herein are particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe embodiments of the invention are apparent from the followingdetailed description taken in conjunction with the accompanying drawingsin which:

FIG. 1 depicts a processing system for implementing the techniquesdescribed herein according to embodiments of the present invention; and

FIG. 2 depicts a node of a multi-node processing system according toembodiments of the present invention;

FIG. 3 depicts a multi-node processing system according to embodimentsof the present invention;

FIG. 4 depicts a drawer of the multi-node processing system of FIG. 3according to embodiments of the present invention; and

FIG. 5 depicts a flow diagram of a method for managing a sharedhigh-level cache for dual clusters of fully connected integrated circuitmultiprocessors according to examples of the present disclosure.

The diagrams depicted herein are illustrative. There can be manyvariations to the diagram or the operations described therein withoutdeparting from the spirit of the invention. For instance, the actionscan be performed in a differing order or actions can be added, deletedor modified. Also, the term “coupled” and variations thereof describeshaving a communications path between two elements and does not imply adirect connection between the elements with no interveningelements/connections between them. All of these variations areconsidered a part of the specification.

In the accompanying figures and following detailed description of thedisclosed embodiments, the various elements illustrated in the figuresare provided with two or three digit reference numbers. With minorexceptions, the leftmost digit(s) of each reference number correspond tothe figure in which its element is first illustrated.

DETAILED DESCRIPTION

Various embodiments of the invention are described herein with referenceto the related drawings. Alternative embodiments of the invention can bedevised without departing from the scope of this invention. Variousconnections and positional relationships (e.g., over, below, adjacent,etc.) are set forth between elements in the following description and inthe drawings. These connections and/or positional relationships, unlessspecified otherwise, can be direct or indirect, and the presentinvention is not intended to be limiting in this respect. Accordingly, acoupling of entities can refer to either a direct or an indirectcoupling, and a positional relationship between entities can be a director indirect positional relationship. Moreover, the various tasks andprocess steps described herein can be incorporated into a morecomprehensive procedure or process having additional steps orfunctionality not described in detail herein.

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as anexample, instance or illustration.” Any embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “at least one”and “one or more” may be understood to include any integer numbergreater than or equal to one, i.e. one, two, three, four, etc. The terms“a plurality” may be understood to include any integer number greaterthan or equal to two, i.e. two, three, four, five, etc. The term“connection” may include both an indirect “connection” and a direct“connection.”

The terms “about,” “substantially,” “approximately,” and variationsthereof, are intended to include the degree of error associated withmeasurement of the particular quantity based upon the equipmentavailable at the time of filing the application. For example, “about”can include a range of ±8% or 5%, or 2% of a given value.

For the sake of brevity, conventional techniques related to making andusing aspects of the invention may or may not be described in detailherein. In particular, various aspects of computing systems and specificcomputer programs to implement the various technical features describedherein are well known. Accordingly, in the interest of brevity, manyconventional implementation details are only mentioned briefly herein orare omitted entirely without providing the well-known system and/orprocess details.

It is understood that embodiments of the present invention are capableof being implemented in conjunction with any other suitable type ofcomputing environment now known or later developed. For example, FIG. 1depicts a block diagram of a processing system 100 for implementing thetechniques described herein. In examples, processing system 100 has oneor more central processing units (processors) 21 a, 21 b, 21 c, etc.(collectively or generically referred to as processor(s) 21 and/or asprocessing device(s)). In aspects of the present disclosure, eachprocessor 21 may include a reduced instruction set computer (RISC)microprocessor. Processors 21 are coupled to system memory (e.g., randomaccess memory (RAM) 24) and various other components via a system bus33. Read only memory (ROM) 22 is coupled to system bus 33 and mayinclude a basic input/output system (BIOS), which controls certain basicfunctions of processing system 100.

Further illustrated are an input/output (I/O) adapter 27 and acommunications adapter 26 coupled to system bus 33. I/O adapter 27 maybe a small computer system interface (SCSI) adapter that communicateswith a hard disk 23 and/or a tape storage drive 25 or any other similarcomponent. I/O adapter 27, hard disk 23, and tape storage device 25 arecollectively referred to herein as mass storage 34. Operating system 40for execution on processing system 100 may be stored in mass storage 34.A network adapter 26 interconnects system bus 33 with an outside network36 enabling processing system 100 to communicate with other suchsystems.

A display (e.g., a display monitor) 35 is connected to system bus 33 bydisplay adaptor 32, which may include a graphics adapter to improve theperformance of graphics intensive applications and a video controller.In one aspect of the present disclosure, adapters 26, 27, and/or 32 maybe connected to one or more I/O busses that are connected to system bus33 via an intermediate bus bridge (not shown). Suitable I/O buses forconnecting peripheral devices such as hard disk controllers, networkadapters, and graphics adapters typically include common protocols, suchas the Peripheral Component Interconnect (PCI). Additional input/outputdevices are shown as connected to system bus 33 via user interfaceadapter 28 and display adapter 32. A keyboard 29, mouse 30, and speaker31 may be interconnected to system bus 33 via user interface adapter 28,which may include, for example, a Super I/O chip integrating multipledevice adapters into a single integrated circuit.

In some aspects of the present disclosure, processing system 100includes a graphics processing unit 37. Graphics processing unit 37 is aspecialized electronic circuit designed to manipulate and alter memoryto accelerate the creation of images in a frame buffer intended foroutput to a display. In general, graphics processing unit 37 is veryefficient at manipulating computer graphics and image processing and hasa highly parallel structure that makes it more effective thangeneral-purpose CPUs for algorithms where processing of large blocks ofdata is done in parallel.

Thus, as configured herein, processing system 100 includes processingcapability in the form of processors 21, storage capability includingsystem memory (e.g., RAM 24), and mass storage 34, input means such askeyboard 29 and mouse 30, and output capability including speaker 31 anddisplay 35. In some aspects of the present disclosure, a portion ofsystem memory (e.g., RAM 24) and mass storage 34 collectively store anoperating system such as the AIX® operating system from IBM Corporationto coordinate the functions of the various components shown in theprocessing system 100.

Turning now to an overview of technologies that are more specificallyrelevant to aspects of the invention, highly distributed, largesymmetric multiprocessing (SMP) systems utilize can share high-levelcache (e.g., L4 cache). Prior SMP systems required tradeoffs to be madebetween the amount of available L4 cache and the level of connectivitybetween processors to accommodate cost and packaging constraints.Existing SMP systems can include multiple drawers, where each drawercontains two independent and separate nodes. These nodes in turn eachcontain multiple central processing (CP) chips (e.g., integratedcircuits) connected together with a dedicated shared cache (SC) chip.Each CP chip is a chip multiprocessor (CMP) with a private L1 and L2cache per processor and one L3 cache shared by all the processors on thechip. The SC chip includes an L4 cache and system interconnect logic.

A drawer of an SMP system can include clusters of CP chips. For example,an SMP system can include one or more drawers, and each drawer caninclude two clusters of CP chips (referred to as “CP clusters”). Each ofthe CP clusters is connected to each other to provide on-drawernode-to-node communication, and also to one of the SC chips on each ofthe other drawers in the SMP system. Existing SMP systems with twoindependent nodes per drawer, each with its own SC chip, maximize theamount of available L4 cache and simplify the SC chip internal designpoint with regard to communications with the attached CP chips. Theattached CP chips in a node are fully connected to each other and alsoto the SC chip in the respective node. Operations originating in any ofthe CP chips are broadcast to all the other CP chips and the SC chip.Many operations can be completed within the node (e.g., a read onlyfetch operation that hits in the L4 cache). While existing SMP systemscan fulfill these operations, any operation that interrogates processorsoutside of the requesting node (e.g., a fetch exclusive that hits in theL4 cache) but observes that the line is shared by another node musttraverse both SC chips to interrogate the other CP cluster in thedrawer, and if it must leave the drawer, this same additional SC chipcrossing is made in every drawer. A workload that can be handled by theprocessors and memory within a single node then performs well onexisting SMP systems. However, workloads that require more processorsand/or memory in a single node can be contained within a single drawer,but in prior SMP systems, these workloads frequently encountered theadded latency imposed by two SC chip crossings to interrogate the cacheson the other node in the drawer.

Turning now to an overview of the aspects of the invention, one or moreembodiments of the invention address the above-described shortcomings ofthe prior art by reducing inter-cluster latencies by using a single SCchip. The single SC chip has a view of the cache on each CP cluster.Accordingly, the single SC chip reduces latency that more than makes upfor any resultant reduction in L4 cache size (as compared to two SCchips).

The embodiments of the present invention utilize SMP system drawers thatcontain two clusters of CP chips connected by a single SC chip. This maybe referred to as dual CP clusters of fully connected chipmultiprocessors with the shared high-level cache. Each CP in a clusteris connected to every other CP chip in the CP cluster and to the SCchip. The SC chip is directly connected to each of the CP chips in bothCP clusters; however, no direct connection exists between chips of oneCP cluster and chips of the other cluster.

To implement a single SC chip architecture in an SMP system, an L4 cachedirectory state in the SC chip tracks cache lines contained in each CPcluster. Indicators for local intervention master (LIM), exclusive (EX),and ownership vector are used to track a state within both CP clusters.These indicators can be implemented in addition to conventionalindicators used to track global states of cache lines relative to otherdrawers in the SMP system, for example.

The above-described aspects of the invention address the shortcomings ofthe prior art by reducing latency within SMP systems. For example, byusing a single SC chip connected to each of the CP chips in both CPclusters, on drawer latency between the CP chips in different CPclusters is reduced. Latency can also be reduced by snooping in a singlecache directory as opposed to sequentially snooping two cachedirectories in two separate SC chips as in previous SMP systems withdual SC chips per drawer. The latency reduction provides significantperformance improvement in SMP systems.

Turning now to a more detailed description of aspects of the presentinvention, FIG. 2 depicts a node 200 of a multi-node processing systemaccording to embodiments of the invention. The node 200 can be a portionof a symmetric multiprocessing (SMP) system, for example, or anothersuitable type of processing system.

The node 200 includes a shared cache 210 that is shared by local noderesources 223 and remote node resources 225 configured and arranged asshown. The local node resources 223 access cache lines 212 in the sharedcache 210 via a cache access interface 222. Similarly, the remote noderesources 225 access cache lines 212 via the cache access interface 222.

FIG. 3 depicts a multi-node processing system 300 including a pluralityof interconnected drawers 301, 302, 303, 304 according to embodiments ofthe present invention. Each of the drawers 301-304 includes two centralprocessor (CP) clusters and a shared cache (SC) chip configured andarranged as shown. For example, the drawer 301 includes a CP cluster311, a CP cluster 312, and an SC 310; the drawer 302 includes a CPcluster 321, a CP cluster 322, and an SC 320; the drawer 302 includes aCP cluster 331, a CP cluster 332, and an SC 330; and the drawer 304includes a CP cluster 341, a CP cluster 342, and an SC 340.

As shown in FIG. 3, each of the SC chips 310, 320, 330, 340 are fullyinterconnected. That is, SC 310 is communicatively connected directly toSC 320, 330, 340; SC 320 is communicatively connected directly to SC310, 330, 340; SC 330 is communicatively connected directly to SC 310,320, 340; and SC 340 is communicatively connected directly to SC 310,320, 330. Although not shown, each SC 310, 320, 330, 340 is alsocommunicatively connected to its respective CP clusters (e.g., the SC310 is communicatively connected to the CP cluster 311 and the CPcluster 312, the SC 320 is communicatively connected to the CP cluster321 and the CP cluster 322, etc.). Additionally, each SC 310, 320, 330,340 includes an L4 cache (not shown).

FIG. 4 depicts a drawer 302 of the multi-node processing system 300 ofFIG. 3 according to embodiments of the present invention. The drawer 302includes two CP clusters (e.g., CP cluster 321 and CP cluster 322). EachCP cluster contains individual CP chips. For example, CP cluster 321contains CP chips 323 a, 323 b, 323 c; and CP cluster 322 contains CPchips 324 a, 324 b, 324 c. Each of the individual CP chips (e.g., CPchips 323 a, 323 b, 323 c, 324 a, 324 b, 324 c) has multiple processingcores (e.g., 2 processing cores, 8 processing cores, 10 processingcores, etc.) and each processing core has its own private L1 and L2cache. The processing cores within each individual CP chip share an L3cache at the CP level. For example, the CP 323 a includes multipleprocessing cores that each has its own L1/L2 cache, and the multipleprocessing cores within the CP 323 a share an L3 cache.

The SC 320 includes interconnects for communication with each CP chip(e.g., CP chips 323 a, 323 b, 323 c, 324 a, 324 b, 324 c) in bothclusters 321, 322 on the drawer 303 and for communication with other SCchips on other drawers (e.g., the SC 310 of the drawer 301, the SC 330of the drawer 303, the SC 340 of the drawer 304, etc.).

The SC 320 also includes an L4 cache 324 and directory that includes theL4 cache and a directory of state bits. For example, the state bits caninclude the following: Global Intervention Master (GIM), which indicateswhich drawer is the intervention master for inter-drawer operations;Global Multi-Copy (GMC), which indicates that the cache line may existon one or more other drawers; Cluster 0 (e.g., CP cluster 321) L4 LocalIntervention Master (Cls1 L4 LIM), which indicates that the L4 cachewill source data for fetches initiated on cluster 0 if set, otherwiseone of the L3's in cluster 0 is the intervention master if the cacheline is a hit; Cluster 1 (e.g., CP cluster 322) L4 Local InterventionMaster (Cls1 L4 LIM), which indicates that the L4 cache will source datafor fetches initiated on cluster 1 if set, otherwise one of the L3's incluster 1 is the intervention master if the line is a hit; Cluster 0 L3Exclusive (Cls0 L3 EX), which indicates that one or more of the L3's incluster 0 may contain newer data than what is currently contained in theL4 cache (no CP's in cluster 1 can have a copy of the line when this bitis set); Cluster 1 L3 Exclusive (Cls1 L3 EX), which indicates that oneor more of the L3's in cluster 1 may contain newer data than what iscurrently contained in the L4 cache (no CP's in cluster 0 can have acopy of the line when this bit is set); Cls0 L3 Ownership Vector, whichindicates which of the L3's in cluster 0 contain a copy of the cacheline; Cls1 L3 Ownership Vector, which indicates which of the L3's incluster 1 contain a copy of the cache line; and L4 Changed Line (L4 CL),which indicates that the data in the L4 cache is changed relative tosystem memory.

The directory states provide for cluster specific local interventionmaster. For example, an L4 intervention master (LIM) to be set toindicate that L4 cache is the data source for fetches. For example, if afetch is received, the LIM designates which CP cluster provides data andprovides “exclusive” cache access. The directory states also provide forcluster specific L3 exclusive bits to indicate that one or more CPs in acluster may have changed data relative to the L4 cache. Clusters canspecify ownership vectors to track ownership both per CP and per CPcluster. The single directory tracks states for two independent clusters(e.g., the CP cluster 321 and the CP cluster 322).

The SC 320 also includes an L4 directory and cache management module 325(hereinafter “module 325”). The module 325 allows for multipleintervention masters, understands when cross cluster interrogation isneeded, understands when cross cluster invalidation is needed,understands when cross cluster memory fetch is needed, accuratelypredicts data source (and target for stores), and tracks potentialchanged data in L3 caches in one of the clusters (e.g., the CP cluster321 or the CP cluster 322).

Module 325 includes logic for implementing rules for various operations.For example, fetch-type operations and input/output (I/O) store-typeoperations can be treated differently and different rules apply to each.

For fetch-type operations, the module 325 can implement the following.As a result of an initial fetch broadcast by the CP 323 a (for example)of the CP cluster 321, the CP cluster 321 L3 LIM (if present) suppliesdata. The CP cluster 321 target memory (if present) speculativelysupplies data if no LIM in the CP cluster 321 exists. The SC 320supplies data from L4 cache 324 if it is L4 LIM and no L3 EX ownerexists in the CP cluster 322. The CP cluster 321 L3 non-requestingowners of a cache line invalidate their respective copies upon receiptof a fetch exclusive or fetch with intent to modify.

Continuing with fetch-type operations, the SC 320 initiates a commandbroadcast to the CP cluster 322 when necessary. When the CP cluster 322is in L3 EX state, it is indicated that an L3 in the CP cluster 322contains newer data than what is in the L4 cache. In such cases, the CPcluster 322 supplies intervention data only if its copy in L3 cache hasbeen changed relative to the L4 cache 324. The SC 320 returns theintervention data from the CP cluster 322 (if any) to the CP cluster 321requester (e.g., the CP 323 a) and updates data in the L4 cache 324. Ifthe CP cluster 322 contains the target memory and the cache line missesthe L4 cache 324, the SC 320 supplies fetch data from the CP cluster 322to the CP cluster 321 requester (e.g., the CP 323 a) and adds it to theL4 cache. When the CP cluster 322 contains a copy of the cache line inany state and the operation is fetch-exclusive (FEX), the SC 320broadcasts an invalidate or interrogate command depending on the EX bitof the CP cluster 322. For example, an invalidate command is broadcastedto the CP cluster 322 if the CP cluster 322's EX bit is off (not set),and an interrogate command is broadcasted to the CP cluster 322 if theCP cluster 322's EX bit is on (set).

Still continuing with fetch-type operations, the SC 320 can update theL4 cache 324 and directory. For example, the ownership bit is set forthe requesting CP, the CP cluster 321 L4 LIM is reset (if on initially),the CP cluster 321 L3 EX bit is set for FEX operations, the CP cluster322 is set for FEX operations, the CP cluster 322 EX status is reset (ifon initially), and the ownership bits are turned off for all but therequesting CP for FEX operations.

For I/O store type operations, the module 325 can implement thefollowing rules for various operations. As a result of an initial I/Ostore type operation by a requester CP (e.g., the CP 323 a) in the CPcluster 321, a target memory chip in the CP cluster 321 manages the I/Ostore sequence to memory if the cache line does not exist in the GIMstate in the L4 cache.

The SC 320 initiates a command broadcast to the CP cluster 321 whenappropriate. For example, if the target cache lines hits any L3 in theCP cluster 321, the SC 320 sends an invalidate command to the CP cluster321. If the CP cluster 321 contains a target memory and it is not therequesting chip, and the line does not exist in the GIM state in the L4cache, the SC 320 manages the I/O store sequence to the L3 memory in theCP cluster 321.

Similarly, the SC 320 initiates a command broadcast to the CP cluster322 when appropriate. For example, if the target cache line hits in anyL3 in the CP cluster 322, then the SC sends an invalidate command to theCP cluster 322. If the CP cluster 322 contains the memory and the cacheline does not exist in the GIM state in the L4 cache, then the SC 320manages the I/O store sequence to the CP cluster 322.

For I/O store type operations, the SC 320 updates the L4 cache directoryas necessary. The ownership bit is turned off for each of the CPs, theL4 LIM bits are set if the cache line exists GIM in the L4 (e.g., theI/O store sequence is completed to the L4 cache), and the L4 directorybits are reset (i.e., the cache line is invalidated) if the cache lineis not GIM initially.

This dual cluster topology provides several benefits. For example, theCPs in a given cluster are fully interconnected with each other and withthe SC chip. Inter-cluster communication flows through one SC chip(e.g., the SC 320) and snoops one L4 directory (e.g., the L4 cache 324and directory). The L4 cache 324 and directory is inclusive of allcaches in both clusters (e.g., CP cluster 321 and CP cluster 322). CPinitiated operations are broadcast to all CP' s in a requester's clusterand to the SC 320. The SC 320 then initiates a broadcast to the othercluster only when needed. This is referred to as “snoop filtering.”

FIG. 5 depicts a flow diagram of a method 500 for managing a sharedhigh-level cache for dual clusters of fully connected integrated circuitmultiprocessors according to examples of the present disclosure. Themethod 500 can be implemented on a suitable processing system, such asthe processing system 100, the multi-node processing system 200, themulti-node processing system 300, or another suitable processing system.

With reference to FIG. 4, the method 500 can occur as follows. At block502, a drawer 302 is provided. The drawer 302 includes a plurality ofclusters (e.g., the CP cluster 321 and the CP cluster 322). Each of theplurality of clusters includes a plurality of processors. For example,the CP cluster 321 includes CPs 323 a, 323 b, 323 c and the CP cluster322 includes CPs 324 a, 324 b, 324 c. The processors (e.g., the CPs) canbe multiprocessors. According to some examples, each of the processorsis connected to each of the other of the processors within itsrespective cluster. For example, the CP 324 a is connected to the CP 324b and the CP 324 c. According to some examples, each of the processorsis connected to the shared cache. For example, each of the CPs 323 a,323 b, 323 c, 324 a, 324 b, 324 c is connected to the SC 320.

At block 504, a shared cache integrated circuit (e.g., SC 320) isprovided to manage a shared cache memory (e.g., L4 cache 324) among theplurality of clusters. The SC 320 can include a directory to storedirectory state bits as described herein. The directory state bits areused to process operations according to sets of rules for processing theoperation based on a type of the operation.

At block 506, the shared cache integrated circuit receives an operationof one of a plurality of operation types from one of the plurality ofprocessors. The operation types can include a fetch type operation, aninput/output store type operation or any other suitable operation.

At block 508, the shared cache integrated circuit processes theoperation based at least in part on the operation type of the operationaccording to a set of rules for processing the operation type. Asdescribed herein, different rules can be applied depending on theoperation type in order to process the operation.

Additional processes also may be included, and it should be understoodthat the processes depicted in FIG. 5 represent illustrations, and thatother processes may be added or existing processes may be removed,modified, or rearranged without departing from the scope and spirit ofthe present disclosure.

The present invention may be a system, a method, and/or a computerprogram product at any possible technical detail level of integration.The computer program product may include a computer readable storagemedium (or media) having computer readable program instructions thereonfor causing a processor to carry out aspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, configuration data for integrated circuitry, oreither source code or object code written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Smalltalk, C++, or the like, and procedural programminglanguages, such as the “C” programming language or similar programminglanguages. The computer readable program instructions may executeentirely on the user' s computer, partly on the user's computer, as astand-alone software package, partly on the user's computer and partlyon a remote computer or entirely on the remote computer or server. Inthe latter scenario, the remote computer may be connected to the user'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider). In some embodiments, electronic circuitry including,for example, programmable logic circuitry, field-programmable gatearrays (FPGA), or programmable logic arrays (PLA) may execute thecomputer readable program instruction by utilizing state information ofthe computer readable program instructions to personalize the electroniccircuitry, in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the blocks may occur out of theorder noted in the Figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdescribed herein.

1.-8. (canceled)
 9. A system comprising: a drawer comprising a pluralityof clusters, each of the plurality of clusters comprising a plurality ofprocessors, each of the plurality of processors comprising a pluralityof processing cores having a private Level 1 cache and a private Level 2cache, the processing cores within each of the plurality of clusterssharing a shared Level 3 cache; and a single shared cache integratedcircuit to manage a shared Level 4 cache memory among the plurality ofclusters, wherein the shared cache integrated circuit is configured tostore computer readable instructions and execute the computer readableinstructions for performing a method, the method comprising: receiving,by the single shared cache integrated circuit, an operation of one of aplurality of operation types from one of the plurality of processors,and processing, by the single shared cache integrated circuit, theoperation based at least in part on the operation type of the operationaccording to a set of rules for processing the operation type.
 10. Thesystem of claim 9, wherein the operation type is a fetch type operation.11. The system of claim 9, wherein the operation is an input/outputstore type operation.
 12. The system of claim 9, wherein the singleshared cache integrated circuit comprises a directory to store aplurality of directory state bits.
 13. The system of claim 12, whereinthe directory state bits are used to process the operation according tothe set of rules for processing the operation type.
 14. The system ofclaim 9, wherein each of the plurality of processors is connected to thesingle shared cache integrated circuit.
 15. The system of claim 9,wherein each of the plurality of processors is connected to each of theother of the plurality of processors within its cluster.
 16. The systemof claim 9, wherein each of the plurality of processors is amultiprocessor.